Real go into the game high on confidence having beaten Barcelona twice in five days. However, with the tie finely poised at 1-1 Mourinho is aware that the small details will be crucial in deciding who emerges victorious.

"I think they will be very defensive when we have the ball and I think it will be the same for us when they have the ball," he said.

"They are a very strong attacking side and we will have to defend stoutly and well when they have the ball.

"Even though we are effectively behind with the away goal we will have to attack and be bold."

Despite Real's form of late, influential midfielder Xabi Alonso insists United's own impressive run of results cancels that out. United have not lost this year, with their last defeat coming on December 5 against CFR Cluj.

"We've enjoyed two days' decent rest (since defeating Barcelona 2-1 on Saturday) but both teams go into the game in decent form,'' the former Liverpool player said.

"I think independent of what has happened in the last week in the two different competitions (Copa del Rey and league) we are coming into the game in good form and so are Manchester United.

"It is a very open tie, we come here knowing we need to score and they know they have to defend properly but it will be very tight and close to call. It is a massive game and will be decisive in both teams' seasons."